1. Field of the Invention
The present invention relates to a wound treatment device with a bandage and heater that are preferably planar, yet flexible, and are connected or joined in a manner that promotes substantially uniform heat transfer from the heater to, and through, the bandage.
2. Description of the Related Art
Wounds, in general, are breaks in the integrity of the skin of a patient. A first type of wound may result from mechanical trauma that produces a cut, tear, or an abrasion. There are many instruments of causality for such wounds, including knives, glass, gravel, or a scalpel. A second type of wound may be caused by a combination of heat and pressure, where the heat alone is insufficient to cause an outright burn. Such wounds include pressure sores, decubitus ulcers, or bed sores, and reflect an injury that is chronic in nature. A wound may also be vascular in origin. In this third type of wound, blood flow through a region may be altered sufficiently to cause secondary weakening of tissues, which are eventually disrupted, thus forming a wound. In the case of arterial causes, the primary difficulty is getting oxygenated blood to the affected area. For venous causes, the primary difficulty is fluid congestion in the affected area, which backs up, decreasing the flow of oxygenated blood. Because these wounds manifest underlying chronic disease processes, such as atherosclerotic vascular disease, congestive heart failure, and diabetes, these vascular injuries also are chronic in nature, forming wounds with ulcerated bases.
Heat therapy has been used to treat wounds since the days of Hippocrates, with varying results. Up to now, heat therapy for wounds has involved the application of heat under conditions that make the tissues of a wound hyperthermic. Hyperthermia impedes wound healing and may actually damage the wound tissues.
The "normal" range of temperature for the human body is 37.degree. C..+-.1.degree. C. (36.degree. C.-38.degree. C.). This is termed the "normothermic" range. Humans exhibit a thermoregulatory response to core temperature changes as little as .+-.0.1.degree. C., wherein "core" as used herein refers to interior portions of the body. This extremely tight temperature control is necessary because virtually all cellular functions, chemical reactions and enzymatic reactions are optimum at normothermia.
Surface tissue varies in temperature according to where on the body it is located. The skin of the torso is usually hypothermic, while the skin of the legs is always hypothermic. The normal skin temperature of the distal leg is approximately 32.degree. C., which is considered to be "moderately hypothermic". The skin temperature of the distal leg of a patient with vascular insufficiency may be as low as 25.degree. C., which is "severely hypothermic". The hypothermic condition of wounds and ulcers inhibits healing. Severely hypothermic skin or wound tissue is in a state that may be termed "suspended animation". In suspended animation, tissue is living, but cellular functions necessary for cell division and collagen deposition are slowed or even stopped. Further, the immune system is inhibited, allowing wounds to become heavily colonized with bacteria. The local application of heat to hypothermic skin will cause some degree of vasodilatation, resulting in an increase in local blood flow. Increased blood flow increases the subcutaneous oxygen tension (PsqO.sub.2) which, in turn, increases collagen deposition and enhances immune function.
Many references report that the immune system is inhibited by hypothermia and activated by mild hyperthermia (fever). Persp Biol Med:439-474, Spring 1980, reports that local body temperature is a critical factor determining host susceptibility, the location of lesions and contracting infectious diseases. New Eng J Med 305:808-814, 1981, reports that animals exposed to cold environments are more susceptible to infectious diseases, whereas exposure to high ambient temperatures often produces a beneficial result. Wound Rep Reg 2:48-56, 1994 and Acta Anaesth Scand 38:201-205, 1994, report that infections caused by a standard inoculum of e. coli or s. aureus were significantly more severe in hypothermic guinea pigs than in normothermic control animals. New Eng J Med 334:1209-1215, 1996, reports that hypothermic colorectal surgical patients had three times more wound infections (19% vs. 6%) than those who were kept normothermic during surgery with a Bair Hugger.RTM. patient warming system described in commonly assigned U.S. Pat. Nos. 5,324,320, 5,300,102 and 5,350,417. Further, six weeks of warming therapy with the Bair Hugger.RTM. patient warming system has successfully healed chronic progressive ulcers which heretofore have been resistant to standard therapies.
Currently available medical devices that apply heat to wounds include infrared lights, warm water pads, warm water bottles, whirlpools and Sitz baths. All types of lesions, such as surgical, chronic, traumatic, donor sites, infected wounds and burns, have been treated with these warming modalities. Particularly difficult has been the application of heat to open wounds such as ulcers. Treatment of a wound with infrared light requires that the wound be positioned under the light during therapy, necessitating patient immobility. Further, the infrared heat causes the wound to dry, thereby slowing the healing process. Warm water pads and bottles and electrical heating pads are cumbersome, reduce patient mobility, and are usually applied to the extremities and held in place with inconvenient wraps such as straps, hook-and-eye material or tabs. Whirlpools and Sitz baths reduce mobility and limit the duration of warming therapy due to skin maceration by the water. None of these modalities is capable of prolonged heat treatment of a wound.